Frequently, situations arise where a meeting between geographically separated parties would be appropriate, but the expenses associated with physical travel are prohibitive to that meeting taking place. The meeting size may exceed available space and gathering all meeting participants in one place is often inefficient. In these situations, industry developed teleconferencing, which provides a convenient, low-cost solution by allowing individuals from various geographic locations to have a meeting over the telephone on the Public Switched Telephone Network (PSTN). While teleconferencing solved some problems, it soon became apparent that teleconferencing is limited to situations where only voice communication is necessary.
In response, industry developed video conferencing systems and data transfer systems on separate networks. These conferencing systems required new and significant hardware, software and programming, and significant communications network connections. For example, stand-alone, “room” systems for audio and video conferencing typically require dedicated hardware at significant expense, in the tens of thousands of dollars, utilizing dedicated video cameras, television or video displays, microphone systems, and the additional video conferencing equipment. These systems also require as many as six (or more) contiguous communication channels. Such communication network capability is also expensive and potentially unnecessary, particularly when the additional channels are not in continuous use. These separate networks have different transport requirements and are expensive to install, maintain, and reconfigure.
As computer technologies advanced, the concept of using voice, data and video over existing IP-based LANs, WANs, intranets, and the Internet emerged. Industry leaders developed IP telephony that enabled multimedia (voice, data, and video) collaboration over a network and it has revolutionized the way society works, entertains, and stays informed. As IP telephony matures and organizations continue to shift from the expensive and inflexible PSTNs to IP-based networks, industry leaders have developed and are developing standards for multimedia communications. The International Telecommunications Union (ITU) is one organization that is developing these standards. One set of ITU standards for multimedia is called H.323.
The H.323 set of standards include standards for data channels, monitoring channels, and control channels. According to the H.323 group of standards, audio and video data streams to be transmitted are encoded (compressed) and packetized in conformance with a real-time transport protocol (RTP) standard. The packets thus generated include both data and header information. The header information includes information whereby synchronization, loss detection, and status detection are facilitated. In order to allow for the exchange of status information between a sender and a receiver, a real-time transport control protocol (RTCP) channel is opened. An H.245 control channel is established to provide control functions. This channel supports the exchange of capability information, the opening and closing of data channels, and other control and indication functions. Within the H.323 standard, video applications may use the H.261, H.262, or H.263 protocols for data transmissions, while audio applications may use the G.711, G.722, G.723.1, G.728, or G.729 protocols. Any class of network which utilizes TCP/IP will generally support H.323 compliant teleconferencing. Examples of such networks include the Internet and many LANs. FIG. 13 illustrates an H.323 inter-network 800.
Four logical entities or components are essential in an H.323 enabled network. These are terminals 802, gateways 806, gatekeepers 808, and multipoint control units (MCU) 810. Terminals, gateways, and MCUs are collectively known as endpoints. An H.323-enabled network can be established with only terminals, but the other components are essential to provide greater practical usefulness of the services. A terminal, or a client, is an endpoint where H.323 data streams and signaling originate and terminate. It may be a multimedia PC with a H.323 compliant stack or a standalone device such as a USB (universal serial bus) IP telephone 818. A terminal must support audio communication 812, 814. Video communication 816 and data 820 communication support is optional.
A gatekeeper 808 ensures reliable, commercially feasible communications. A gatekeeper provides central management and control services. When a gatekeeper exists, all endpoints (terminals, gateways, and MCUs) must be registered with it. Control messages are routed through the gatekeeper. The gatekeeper provides several services to all endpoints in its zone. These services include address translation, admission and access control of endpoints, and may provide bandwidth management, call routing capability, and control of media routing. A gatekeeper can route all calls originating or terminating in its zone, and may control media routing of those calls. A gatekeeper that controls media routing also acts as a multipoint controller (MC). This capability provides numerous advantages. Gatekeepers map LAN aliases to IP addresses and provide address lookups when needed. Gatekeepers also exercise call-control functions to limit the number of H.323 connections and the total bandwidth used by these connections, in an H.323 zone. A gatekeeper can re-route a call to an appropriate gateway based on bandwidth availability.
A gateway 806 is an optional component in a H.323-enabled network. Gateways bridge H.323 conferences to other networks, communications protocols, and multimedia formats and provides data format translation, control signaling translation, audio and video codec translation, and call setup and termination functionality on both networks. Gateways are not required if connections to other networks, such as a PSTN 420, or non-H.323-compliant terminals are not needed.
A multipoint control unit (MCU) 810 enables conferencing between three or more endpoints. It consists of a mandatory multipoint controller (MC) and zero or more multipoint processors (MP). The MCU may be combined into a terminal, gateway, or gatekeeper. In cases where the gatekeeper contains a MC, the MC component of the MCU may act as a slave MC under control of the gatekeeper's MC. The multipoint controller provides a centralized location for media control channels of a multipoint conference setup. Media control signaling is routed through the MC so that endpoints capabilities can be determined and communication parameters negotiated. The MC may be used in a point-to-point call which can later be extended into a multipoint conference. When there is a change in the number of participants in the conference, the MC can determine the distribution topology to use for the audio and video streams depending on the multicast capability of the underlying network, the capabilities of MPs in the network, the capabilities of the terminal endpoints, and the physical topology of the network with respect to the terminal endpoints and MP endpoints of the multipoint conference. The multipoint processor handles the mixing, switching, and processing of the audio, video, and data streams among the conference endpoints. The MCU is necessary in a centralized multipoint conference where each terminal establishes a point-to-point connection with the MCU. The MC component of the MCU determines the capabilities of each terminal and MP component of the MCU sends each terminal a processed media stream. In the decentralized model of multipoint conferencing, a MC ensures communication compatibility, but the media streams are multicast and mixing is performed at each terminal. It should be noted that media distribution in a multipoint conference may be a hybrid of centralized and decentralized distribution modes, media may be distributed through multiple MPs, and distribution may be via multicast network capabilities in some, all, or none of the branches of the conference.
In either type of multipoint conferencing, there are multiple audio and video streams and these streams could be coming from various sources and processing requirements for the streams may be different. For these streams to be seen by all participants, the streams may need to be transcoded to formats that participants are capable of seeing. If this could not be done for a particular participant, that participant could not participate in the conference. In order to allow all potential participants to participate in a conference, the MCU and the gateway has to have the capability to perform the transcoding that may be required. One shortcoming of this is that the MCU or gateway has to be a mammoth service provider to perform the transcoding that may be required. A further drawback is that the MCU or gateway would have to be in complete control of the media for the entire multipoint conference and know exactly what has to be done with the media.
A method is needed whereby the computational resources of specialized terminals are used to transcode data from one format to another or apply signal processing operations to the data in its native format, thereby freeing up resources for the MCUs and gateways.